Reduced airway inflammation, mucus production and airway remodeling in map kinase-activated protein kinase (MK2) knockout mice

Abstract

Rationale MAP kinases play an important role in immune and airway cells. MK2 is a kinase that functions downstream of p38 MAP kinase. We investigated asthma phenotype in MK2 knockout mice. Methods MK2 knockout and littermate control (129/C57B/6) mice were immunized with ovalbumin. Following an inhalation challenge airway inflammation, mucus production and extracellular matrix (ECM) deposition were assessed by H&E, PAS and Trichrome staining, respectively. Molecules regulating inflammation, mucus production and tissue remodeling were examined by real-time PCR and immunostaining. Results MK2 knockout mice showed significant reduction in airway inflammation, mucus production and ECM deposition. Reduced inflammation was associated with decreased lung mRNA for many cytokines (IL-5, p<0.004; IL-9, p<0.006; IL-10, p<0.02; IL-13, p<0.03; IL-25, p<0.008). Reduced Th2 cytokine expression was associated with diminished phospho-STAT6 staining in airway epithelium and infiltrating cells. Interestingly, mRNA for CC chemokines (MCP-1 & MCP-3) was not decreased. Reduced mucus production correlated with decreased mRNA for MUC5AC (p<0.04) and the mucus regulatory gene CLCA3 (p<0.05). Low ECM deposition was concomitant with reduced smooth muscle-actin (a marker of myofibroblasts) and phospho-Smad1 (a profibrotic signaling molecule). MK2 secondarily affects p38 expression, which was decreased in knockout animals. Therefore, the knockout phenotype is the result of complete absence of MK2 and partial loss of p38. Conclusions The p38-MK2 pathway plays an important role in airway inflammation, mucus production and ECM deposition in a mouse model of asthma. Although many phenotypic outcomes are likely due to reduced inflammation, others (reduced phospho-Smad1 and ECM deposition) could be partially attributed to MK2 loss in airway cells.